Field of the Invention
The present invention concerns a method in order to implement an RF excitation with two resonance frequencies by operation of a magnetic resonance (MR) system in order to detect or, to quantify the CEST (Chemical Exchange Saturation Transfer) effect.
Description of the Prior Art
In MR imaging, the CEST effect is utilized in order to indirectly detect specific substances (for example creatine, glycogen, glutamate). Use of the CEST effect makes it possible to better assess and evaluate the quality of cartilage of a human examination subject, for example, than is possible via other methods for MR imaging.
The transfer of magnetization via chemical exchange is utilized in CEST. The resonance signals of labile protons, which are bound in molecules of the substance to be detected, are saturated in order to detect these protons when they are subsequently bound to water molecules to which they have been transferred via chemical exchange.
However, conventional magnetization transfer (MT), in which two different sets of spins exchange their magnetization (more precisely their magnetic polarization), still exists in addition to CEST. In the field of MR imaging, MT is a magnetization transfer in which one of the two sets of spins represents water (more precisely water protons), which is present in large quantities in tissue and organs in the human body. The other set of spins represents protons that are bound in molecules of the substance to be detected.
Since CEST and MT occur simultaneously in human tissues and organs, it is difficult to qualitatively, or better, quantitatively, measure the effects of the CEST effect alone (i.e. without influence of MT).